EXPLANATION OF PLATES. 



KEY TO LECiEXDS IN FIGURES. 



ah, Undest'ribcd nucleus (I'f. text, p. 27) (orange). 



ac, Nucleus alsc cinereir (purple). 



am, Nucleus ambiguus (uncnlored). 



ar, Nucleus arciformis (yellow). 



eg, Substantia grisea centralis (uncolorcd). 



CO, Nucleus nervi cochlea! (purple). 



cii, Nucleus fasciculi cuneati (red). 



fr, Formalio reticularis (luicolored). 



ft, Nucleus funiculi teretis (green). 



gr. Nucleus fasciculi gracilis (yellow). 



in, Nucleus intercalatus (blue). 



ic, Nucleus incertus (purple). 



la. Nucleus lateralis (green). 



tnc, Anterior motor column (red). 



oil. Nucleus olivaris accessorius dorsalis (orange). 



ol, Nucleus olivaris inferior (uncolored). 



oin. Nucleus olivaris accessorius medialis (orange). 



OS, Nucleus olivaris superior (violet). 



pb. Corpus ponto-bulbare (yellow). 



po, Nuclei pontis (yellow). 



TO, Nucleus of Roller (green). 



Is, Nucleus tractus .solitarii (uncolorcd). 



vc, Nucleus nervi vestibuli (green). 



vm, Nucleus motorius nervi trigemini (uncolorcd). 



vs. Nucleus sensorius nervi trigemini (blue). 



vi, Nucleus nervi abducentis (red). 



vii, Nucleus nervi facialis (uncolored). 



xii, Nucleus nervi hypoglossi (red). 



Fig. 1. Drawing of the ventral aspect of the whole model (X 7.5). The heavy pontine mass is prolonged 

 caudally in the form of intcrrujited arcuate nuclei. The latter bow away from the mid-line on both 

 sides and lie in front of the two oliva". At their termination the anterior columns of the spinal cord 

 extend to the base of the model. The outlines mark the configuration of the brain-stem and end 

 cephalad to the lateral recess, .\long the margins are given the levels of the sections, represented 

 in figures 8 to 14. 



Fig. 2. Drawing of the left lateral aspect of the model (X 7. .5). The prominent pontine nuclei overhang 

 the olive and an arrow passes through the roughened tunnel in the graj- material formed by the 

 pyramidal tract in its crossing. The ventral limit of the brain-stem is outlined in its entire extent. 

 Dorsally the margin is discontinued at the dorsal (Cochlear nucleus, where it runs toward the cere- 

 bellum as the anterior wall of the lateral recess. 



Fig. 3. Drawing of the dor.sal aspect of the model (X 7.5). To the right of the mid-line, the nuclei of the 

 upper cervical cord are rc[)resented, but where the central canal expands into the fourth ventricle 

 the smooth surface of the floor has been retained. On the left side, all the nuclear masses have been 

 modeled separately. The ink line marks out the configuration of the brain-stem as far as the outline 

 is not a knife cut made in preparing the specimen. 



Fig. 4. Drawing of the mesial aspect of the left half of the model (X 7.5). The pontine mass, the nucleus 

 reticularis tegmenti pontis, and the caudally projecting arcuate nuclei are represented as trans- 

 parent. The central canal of the spinal cord is shown in dotted lines which are continued into the 

 fourth ventricle as far as the nucleus intercalatus. The surface form is represented in outline on 

 the ventral side, while dorsally this line is continued in the region of the anterior wall of the lateral 

 recess, as in figure 2. 



Figs. 5, 6, 7. Drawings of the ventral, mesial, and dorsal aspects, respectively, of the nucleus olivaris 

 inferior (X 7.5). The first, second, and third primary fissures arc designated in these figures by 

 the constant initials of a, b, and c, on the ventral and dorsal surfaces. The form and jjosition of 

 the nucleus olivaris accessorius dorsalis is portrayed by a simple outline. 



Figs. 8, 9, 10, 11, 12, i:i, 14. Drawings of cross-section (X 2.4) representing respectively sections 5, 2()(), 

 400, 500, ()()0, 700, and 900, which have been selected from the series used in this reconstruction. 

 The accom[)anying outline drawings show the limits of the nuclear masses, with the same color 

 representations as in the other figures. The iiosition of these sections in the model is given by 

 the various section-levels in the first four figures. 



78 



